1. Field of the Disclosure
The present disclosure relates, generally, to a resistive memory device having a resistor part for controlling a switching window, and, more particularly, to a resistive memory device that additionally includes a resistor part for controlling a switching window, thus assuring a sufficiently large switching window, resulting in excellent operational reliability.
2. Description of the Related Art
In general, a large number of electronic memory devices include a bistable element to cause switching from high resistance to low resistance or vice versa upon the application of voltage. In particular, a resistive memory device means memory having resistance that varies with the applied voltage and storing data corresponding to such variations in resistance, as a concept contrasting with capacitative memory devices.
Chalcogenide materials, semiconductors, and various types of oxides and nitrides are known to have resistive memory properties. Further, it has been found that some organic materials have resistive memory properties. Although the resistive memory devices are disadvantageous because they have high driving voltage and current, low durability, and low thin film handling properties, the above problems may be overcome with the recent rapid development of material engineering technologies. Thus, resistive memory devices are receiving attention as multi-bit operating memory, which is nonvolatile and has low power consumption and high density. Examples of the resistive memory device include phase change RAM, organic memory, oxide resistive RAM, etc.
Of these memory devices, organic memory is composed of a memory matrix including a lower electrode, an upper electrode, and an organic memory layer sandwiched between the lower and upper electrodes, in which a cell, formed at the position where the upper electrode overlays the lower electrode, provides the bistable properties.
In the resistive memory device, a memory cell typically exhibits two resistance states, that is, a low resistance (set) state and a high resistance (reset) state, in which if the low resistance state is defined as data “1” and the high resistance state is defined as data “0”, the two logic states of data may be stored in the memory cell. Such two states may be switched by application of voltage or current. As such, a difference in voltage or current between the two states is referred to as a switching window.
However, at present, it is difficult to assure the switching window in oxide resistive RAM or organic memory. In particular, organic memory is more severely problematic due to the wide driving voltage distribution. FIG. 1 is a graph showing the results obtained by measuring only the voltages corresponding to the set-reset states through the voltage sweep following the application to organic memory. From FIG. 1, it can be seen that the switching window is difficult to assure due to the wide driving voltage distribution.
In the resistive memory device, a difference between the voltage (current) inducing the set state and the voltage (current) inducing the reset state should be sufficiently ensured so as to enable reliable operation of the device. However, conventional resistive memory devices have problems in being incapable of ensuring the switching window, resulting in decreased operational reliability of the device.